I don't think that empty space down the center of the image works. It feels a bit like where the spine of the book goes in a wrap-around book cover image._________________Art Links Archive -- Artists and Tutorials

I think two biggest issues here is lighting and composition. I took the liberty of doing a little rough repositioning and overpaint if you can call it that to demonstrate some of my comments - I hope you don't mind.

1. The image is too dark, I just tweaked the levels a bit to demonstrate the point and through some light over it (edit: though having looked at it for a few minutes i'm not so sure whether its an improvement..)
2. The right wing is massive and seems to throw the figure off balance. Pulled it in to demonstrate
3. The composition of the image is thrown off by the big grey area in the middle, I did a little rough re-composition of the castle and the bridge in relation to the figure and it looks better to me
4. Sword is held at an awkward angle and looks out of place, changed the angle a little bit

These opinions are just that - my own take on how to improve it, plus I'm not particularly good, so take it with a grain of salt. Hope it helps.